Optical pickup of a planar image source, for example a screen, which may be implemented as a scintillator screen, may be performed using one or more cameras. Such a pickup of a screen is achieved, for example, by an X-ray camera which may be employed in digital radioscopy, for example for product quality control.
In medical radioscopy, so-called flat-panel detectors are currently used. In such flat-panel detectors, X-radiation is typically converted to visible light via a scintillator screen, and said visible light is then identified via a semiconductor layer arranged directly behind the scintillator screen in the beam direction and usually consisting of amorphous silicon, and is converted to an image. The efficiency of a scintillator screen depends, among other things, on the adjusted energy of the X-ray quanta. The higher the energy of the X-radiation, the fewer X-ray quanta will be absorbed in the scintillator and will contribute to the image. The non-absorbed X-ray quanta may be absorbed by the underlying semiconductor layer, thereby damaging same. Given an appropriate dose, this radiation damage will eventually cause the detector to fail.
The field of medicine also uses detectors wherein the X-radiation is initially converted to visible light by a scintillator, too. However, said visible light is subsequently imaged in an optical manner, e.g. onto CCD cameras.
German patent DE 10301941 B4 shows a camera for optically picking up a screen, the screen comprising an area, and a predetermined overall resolution being envisaged for the optical pickup, comprising a camera support having an array of camera mounts, an array of individual optical cameras, each individual optical camera being fixedly attached to an associated camera mount, an individual optical camera comprising a light sensor and an optics imaging means, the light sensor and the optics imaging means being operative to pick up a subarea of the screen area at an individual resolution higher than the overall resolution, and comprising an image processing means for processing individual digital images of the array of individual optical cameras so as to generate the optical pickup of the screen at a predetermined overall resolution, the image processing means being operative to subject the individual digital images to a correction so as to reduce alignment inaccuracies and/or parameter variations in the array of individual optical cameras, a correction specification being used, for the correction, which is intended for an individual image with a calibration, and the correction taking place at a correction resolution which is higher than the predetermined overall resolution and is lower than or equal to the individual resolution so as to obtain corrected individual images or a corrected overall image, and to combine adjacent pixels of the corrected individual images and to then compose the images, or to combine adjacent pixels of the corrected overall image in order to obtain the optical pickup having the predetermined overall resolution.
EP 0862748 A1 describes an arrangement wherein the visible light emanating from a scintillator is laterally deflected via a V-shaped mirror arrangement. This lateral deflection results in that the optical light path behind the mirror is essentially parallel to the scintillator screen. Because of this, radiation-sensitive cameras may be arranged outside the X-ray path, and radiation damage may be avoided at the same time. Such an arrangement is shown in FIG. 6, for example. In particular, there is a scintillator 600, opposite which the V-shaped mirror arrangement 602 is arranged. The mirror arrangement 602 deflects the light received by the scintillator 600. Two sensors 604, 606 are located within the light path of the deflected radiation, the sensor 604 imaging a first subregion 600a, whereas the second sensor 606 images a second subregion 600b of the scintillator screen. The lateral arrangement of the sensors 604, 606 additionally enables reduced structural height of the arrangement, so that this arrangement may be integrated into conventional film cartridges.
A further alternative to the arrangement shown in FIG. 6 is depicted in FIG. 5. Here, only a single mirror 603 is arranged, which images the entire scintillator 600 on a single sensor camera 605. In this case, too, the sensor 605 is arranged laterally in relation to the scintillator.
What is disadvantageous about the concept depicted in FIGS. 5 and 6 is that the structural height perpendicular to the scintillator screen is reduced since the sensors are arranged laterally. But the lateral arrangement of the sensors has the disadvantage, in turn, that the lateral dimension of the X-ray camera increases considerably. For example, in the concept shown in FIG. 6 the structural size of the X-ray camera is no longer determined by the scintillator screen 600, but by the space that may be taken up by the two sensor cameras 604, 606 and by the minimum distance of the two sensor cameras 604, 606 from the V-shaped mirror 602 so that the optical imaging conditions are achieved. As compared to the implementation wherein the semiconductor layer is arranged directly behind the scintillator screen, the length of the X-ray camera therefore increases considerably.